Pets May Prevent Allergies

Pets May Prevent Allergies, Not Cause Them

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You may have heard that infants who grow up in households with pets can develop resistance to allergies — and a new study may have nailed down why.

Research suggests that exposure to all sorts of dirt and dander is beneficial in terms of exposing a child's immune system to, and strengthening it against, various allergens; as researcher Ganesa Wegienka put it, "Dirt is good." And children who live with — read: "roll around and play with" — dogs and cats are less likely to become allergic to those animals later in life, as long as the exposure occurred during the first year of life. The study appeared in the journal "Clinical & Experimental Allergy," and followed over 500 kids until age 18; teens who had lived with a cat during their first year had a 48 percent lower risk of developing a cat allergy. Meanwhile, teen boys who had lived with a dog were 50 percent less likely to develop dog allergies — but the rate was not the same for infant/teen girls who had lived with dogs, for reasons researchers still don't quite grasp. (They theorize that baby boys may play with dogs differently.) Keep reading for more details.

These results make intuitive sense, based on a layperson's understanding of the immune system and how it learns to protect us. Certainly they allow expectant parents to breathe a sigh of relief; worries about your human baby's breathing don't have to mean giving away your furry babies, or quarantining them in the basement rec room. But how exactly does it work? Researchers at the University of California San Francisco may have an answer, in a paper that was presented at the annual meeting of the American Society for Microbiology in San Francisco.

After exposing mice to dust from pet-owning houses, scientists working with lead researcher Kei Fujimura found that those mice appeared to be protected against a virus called respiratory syncytial virus (RSV). RSV is common; it infects the lungs and breathing passages, and causes respiratory illness in kids (it tends to manifest as a regular head cold in adults). Severe cases of RSV in babies are associated with higher rates of respiratory problems like asthma later.

The mice exposed to pet-house dust, then exposed to RSV, didn't get RSV symptoms like lung inflammation or increased mucus — and when researchers looked at the microbes living in the guts of those mice, they found different bacteria from those in the guts of mice who did get infected. Bacteria in the digestive system might not seem to have anything to do with problems in the respiratory system, but scientists say it's all part of a larger system called the "microbiome" — the entire population of bugs and bacteria, good ones and bad ones, living on and in humans. This microbiome starts acquiring members of this "community" when we're born, as we're being born, and after that, everything we're exposed to affects the microbiome's composition. What we're exposed to as babies, then, may help protect us later on — in other words, all the dog hair your kids accidentally ate during their crawling days may be why they're not allergic to dogs now.

And the thought of our kids ingesting shedded fur is pretty gross — but it could have big implications for curbing childhood asthma. Fujimura said in a statement about the study that microbes could "colonize the GI tract, modulate immune responses, and protect the host against an asthmagenic pathogen, RSV"; past studies have indicated that kids who grow up in rural environments — i.e., around livestock — have a lower likelihood of developing asthma and allergies than "city kids" do.

Fujimura noted that there's more work to be done in terms of identifying the specific microbes and "mechanisms" that create a protective effect in pet-related house dust, and every kid is different (not to mention different from a mouse). So, nestling the baby in a basket of kittens "for her health" sounds tempting (and adorable!), but as usual you should ask your pediatrician about symptoms and prevention.
But if you thought the dog was going to make the baby sick, it could be just the opposite.